Most likely citrus leaf miner. Tiny moths lay eggs on the underside of the leaves - one egg per leaf. The eggs hatch and the larvae burrow between the layers of the leaves, causing deformation and leaving squiggly trails. Unsightly, but not deadly unless it affects a large percentage of the leaves. The eggs are only laid on new growth, so you're better off pruning only once a year. If you keep trimming the ugly leaves off, new ones will grow and attract more miners. They are seasonal, so they're eventually go away. Spray doesn't do much because the larvae are inside the leaves. Some people use an imidacloprid (sp?) drench, but I wouldn't use a systemic insecticide on something I was going to eat. Bottom line - ignore it. Next year you can also try a pheremone trap placed away from the tree.

I have to disagree with the comment that sprays don't do much. I use a Spinosad spray when new leaves start growing (so 2-3 times a year, minus the first new leaves of the year which normally grow before leafminers show up). It works flawlessly as long as you spray before the miners start tunneling, or shortly after they start. Much less dramatic than an insecticide drench.

Thank you so much Igteacher and Humsi for the very detailed information about the leaf miner problem we are having on the lemon plant. I very much appreciate your response and the advice. I am sorry for the delay in my reply.

Chitra